The present invention relates to data storage systems, and more particularly, this invention relates to a caching scheme for extent migration.
In current hybrid tiered-storage systems, higher level solid state device (SSD) tiers suffer caching performance problems with respect to sequential-writes, as the current caching algorithms in place, such as CLOCK, CSCAN, WOW, etc., are tier ambiguous, and typically designed to leverage spatial locality, which is a performance consideration for hard disk drives (HDDs). One of the draw-backs of this configuration is that although these algorithms work well for HDDs (e.g., in reducing platter seeks), they are not suited for SSD device pools in a tiered-storage environment.
In a typical hybrid SSD/HDD tiered-storage system, SSDs display their greatest performance improvement over HDDs in performing random write operations. However, with only one ambiguous (non tier-specific) caching algorithm in-place, SSD tracks exhibiting this property are not optimally cached (e.g., due to a lack of hits), thus reducing the overall system performance. Another drawback of utilizing a singular cache and algorithm for multiple tiers is that there is no practical method of mapping a specific caching algorithm to a specific tier, thus optimal caching cannot be achieved.
Therefore, a method, such as a caching scheme, which utilizes and takes advantage of the improved performance of SSDs in a hybrid HDD/SSD tiered-storage system would be very beneficial to the field of data storage. Moreover, use of such a caching scheme in other tiered-storage systems may also be desirable.